In the conventional manufacture of a rubber footwear product, uncured rubber or rubber coated fabrics are typically milled or extruded into the appropriate thicknesses from which the desired sized component parts for the footwear product are cut. The assembly of uncured components are normally formed upon a forming device such as a metal last. The metal last bears the internal shape and size of the desired footwear product. The last is normally of a heat conductive metal construction such as hollowed, shoe or boot-shaped aluminium form. Pursuant to such manufacture, it is conventional to assemble an uncured rubber upper portion, an uncured conventional rubber insole, an uncured foxing band (e.g. a flat uncured strip), an uncured rubber binder (e.g. uncured sheeting stock or filler) and a precured rubber sole coated upon the forming last. This completed footwear assembly is then vulcanized to provide the desired rubber footwear vulcanizate product.
In a typical assemblage, an uncured shoe or boot upper is positioned so as to adhesively overlap the insole upon the last. An uncured foxing band or flat band (e.g. 1-2 inches in width) is then placed around the outer periphery or rim of the rubber upper followed by the emplacement of an uncured binder or filler onto the insole. The binder or filler will not normally extend beyond the exposed surface of the insole. An uncured rubber outsole is then wrapped over the projecting edge of the insole onto the uncured rubber upper above the feather line. The uncured rubber assembly (which appearance is of a crude footwear) is then vulcanized, typically for about 1 to 2 hours at temperatures ranging from about 250.degree.-350.degree. F. upon the last to provide the vulcanizate product. The component parts are thereby chemically and physically melded into a complete vulcanizate footwear product of unitary construction.
Uncured or unvulcanized rubber (natural or synthetic) footwear components normally posses sufficient tack for assemblage upon the forming last. An uncured rubber formulation generally includes ethylenically unsaturated polymeric substances in combination with conventional vulcanization or curative additives. Included amongst such conventional additives are crosslinking reagents such as sulfur, accelerators, tackifiers antioxidants, activators, etc., which permit the formulation to be cured into a vulcanizate product. The additives and polymeric rubber substances are usually admixed in a Branbury mixer and then formed into the desired thickness or shape of the footwear component parts. This is usually accomplished by milling, extruding, calendering techniques, etc. without curing the rubber formulation.
Vulcanization of the uncured assemblage alters the chemical and physical attributes of the rubber composition via crosslinkage of the ethylenically unsaturated polymeric linkages with the crosslinking reagent. Cross linkage occurs not only within each of the individual assembled component parts but also between those ethylencially unsaturated polymeric molecules positioned at the interface of the adhesively overlapped component parts. This melds the component parts into a vulcanizate product of a unitary construction.
Heretofore, the conventional manufacture of such rubber footwear products necessitated vulcanization of the entire assemblage. Such a manufacture has placed severe constraints upon the rubber footwear manufacturing industry. Thermoplastic and other natural or synthetic polymeric substances thermally sensitive or degradable upon vulcanization were not acceptable for use in such a manufacture. Outsoles for such footwear products were essentially limited to those of a rubber vulcanizate construction. Such constraints made it difficult for the rubber footwear industry to effectively compete against other footwear products, the later of which manufacture permits more fashionable designs (e.g. high heeled shoes, western boots, contrasting sole colors, etc.) at a low cost. Footwear of a lightweight construction, replaceable or repairable soles, speciality soles adapted for specific uses (e.g. spiked, cleated, ridged soles such as for golf, football, hiking, baseball, etc.) or other speciality wear features were not feasible under the existing technology of such rubber footwear manufacture.
It would desirable for the rubber footwear industry to be able to incorporate many of the desirable attributes of such other footwear products into a footwear vulcanizate while preserving many of its other desirable attributes such as resistance towards air, gas, sunlight, hydrocarbon, moisture penetration, fats and oils, acid and other chemicals, along with its excellent durability of wear, strength, elasticity, electrical and heat insulation, structural integrity properties, etc. A uniquely different method of manufacturing rubber footwear products would be desirable especially if it were able to provide footwear products uniquely different in construction, utility and design. Rubber vulcanizate footwear products suitably adapted to separately receive an outsole would afford significant labor, equipment, production time and material savings. Notwithstanding a long felt need for uniquely different rubber vulcanizate footwear products and manufacture thereof, the manufacture of rubber footwear vulcanizates has remained essentially unchanged since the beginning of this century.
The athletic sports footwear product (e.g. tennis shoes, etc.) manufacture, generally differs from those products of the rubber vulcanizate manufacture in that it frequently includes a polyurethane outsole construction. Such outsoles are normally incorporated into the athletic footwear by injection molding techniques. U.S. Pat. No. 4,245,406, by Landay, discloses a sport shoe having an outsole comprised of an injection molded polyurethane midsole construction to which there is attached a rubber outer sole. Similarly, U.S. Pat. No. 4,455,765, by Sjosward, discloses an outsole with a polyurethane midsole sport shoe product with a rubber outer sole. A patent issued to Giese U.S. Pat. No. 4,366,634) discloses an injection molded sport shoe, such as a tennis shoe, having a fabric upper portion secured to a sidewall with an outsole constructed of two different materials (preferably rubber and a polyurethane midsole) to which there is bonded a rubber outer sole. Another variation involving polyurethane shoe construction is disclosed by U.S. Pat. No. 4,228,600 by Kruge. The Kruge shoe bottom is disclosed as comprising a flexible, closed-cell, crosslinked polyolefin foam having at least one surface of exposed open cells and an elastomeric polyurethane film which encompasses the foam.
A method for manufacturing a ski boot constructed of an upper part and a prefabricated sole is disclosed in U.S. Pat. No. 3,273,263 by Kilma. The prefabricated sole of Kilma includes a metal plate adapted to receive notched nails or screws embedded within the sole. The sole is secured to the ski boot by means of glue and nails or screws. In another U.S. Pat. by Denu (No. 4,130,947) there is disclosed a method of making a sole wherein a layered substance resistant to abrasion is vulcanized onto a dampening layer of a synthetic or natural rubber.
U.S. Pat. No. 2,983,643 by Seiberling discloses a heel obstensibly suitable for adaptation to footwear constructed of leather uppers. Seiberling mentions, in column 1, lines 25-32, the unique difficulties typically encountered when it is desired to adhesively bond a cured rubber heel to another surface. According to Seiberling, it is customary to abrade the skin surface of the cured rubber to roughen it, otherwise the cured skin becomes so slick that it does not form a good bond with the adhesive. The roughened surfaces of the cured rubbers may then be adhered to another surface by an adhesive. Seiberling proposes to avoid the need for roughening by incorporating cellulosic fibrous materials into that portion of the heel surface to the glued (e.g. animal glue) onto the shoe. This is reportedly accomplished by placing an uncured or raw rubber biscuit with an overlying fibrous mat into a mold, which is then vulcanized into a heel vulcanizate having embedded cellulosic fibrous projections upon the glueing side.
A European patent specification by Phillips (Publication No. 0 075 861) further illustrates the attendant problem in repairing leather footwear with thermosetting butadiene-styrene half soles. Phillips proposes to overcome this problem by imparting a pebbled surface texture onto the half sole. The pebbled surface reportedly enhances the adhesive properties of the sole and facilitates the application of a hot melt adhesive thereto.